• The Journal of Korean Association of Computer Education
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• v.5 no.1
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• pp.57-66
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• 2002

Real time multimedia data services have been made possible by the rapid development of the computer and internet technology. Based on the technology, Many multimedia system developer try to use VOD(Video on Demand) and GVA technologies for distance education. However the system has mainly been developed to provide the video screen of good quality in real time and to compose contents efficiently. Not many researches and developments have been made for providing the users that is taking distance education with various types of service using VOD and GVA. Therefore In this paper we have designed and implemented an active on-demand multimedia service system to improve user-side service quality in distance education using VOD and GVA service. The on-demand multimedia service system can prominently help users to save the time and effort to search and select the studying data by this paper enables off-line search functions through E-mail and periodical current awareness service supported by PUSH technology, user oriented information booking supported by SDI service and feedback service.

• International Journal of Highway Engineering
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• v.12 no.4
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• pp.211-218
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• 2010

Volume of concrete slab changes by temperature and moisture effects. At that time, tensile stress develops because the slab volume change is restrained by friction resistance between the slab and subbase, and then crack occurs occasionally. Accordingly, researchers have made efforts to figure out the friction characteristics between the slab and subbase by performing push-off tests. Lately, researches to analyze concrete pavement behavior by the friction characteristics have been performed by finite element method. In this study, The friction characteristics between the slab and subbase were investigated based on the friction test results for lean concrete, aggregate, and asphalt subase widely used in Korean concrete pavements. The energy method bilinearizing relation between nonlinear friction resistance and displacement were suggested. The friction test was modeled by 3-D finite element program, ABAQUS, and the model was verified by comparing the analyzed results to the test results. The bilinear model developed by the energy method was validated by comparing analysis results obtained by using the nonlinear and bilinear friction resistance displacement relation as input data. A typical Korean concrete pavement was modeled by ABAQUS and EverFE and analyzed results were compared to evaluate applicability of the bilinear model.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.6D
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• pp.719-726
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• 2009

In this study, a series of push-off tests for lean concrete, aggregate, asphalt subbases mainly used in Korea were performed to investigate the friction characteristics between the slab and subbase layers. Use of separation membrane and wet condition of subbase were other parameters in the tests. Horizontal displacements of the slabs and friction coefficients were measured at 1st loading, stable condition (2nd and 3rd loadings), and wet condition (4th loading) by applying 40mm/hour horizontal loadings. Larger maximum friction coefficients were measured in order of the lean concrete, asphalt, aggregate, and subbases using the separation membrane at 1st loading, and in order of the asphalt, aggregate, lean concrete, and subbases using the separation membrane at stable and wet conditions. The friction coefficients of the aggregate and asphalt subbases which did not used the separation membrane decreased by the wet condition while the subbases using the separation membrane were not affected. Additional push-off tests for effects of slab thickness and temperature sensitivity of asphalt will be performed. And, effects of the friction characteristics between the slab and subbase layers on behavior and performance of concrete pavements will be investigated by structural analyses using the test results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.1
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• pp.6-16
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• 2009

For the application to the direction finding(DF) antenna for V/UHF bands, circular active array composed of 9 dipole element has been investigate. For miniaturization of the overall size array, the element has been chosen to be of the top-hat dipole type. For the broadband operation over 20-1300MHz, some number of pin diodes have been inserted in each arms of each dipole element. By employing this type of each element dipole, the effective dipole length can be increased or decreased according as the inserted pin diodes is on or off. The active array antenna has been design to be directly connected to the balanced push full amplifier such that the amplifier may play a role as a balloon and may improve the sensitivity as a receiver as well. The active array antenna has been designed and fabricated. Some experimental results have been presented in comparison with simulated results.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.94-100
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• 2016

A novel optical design for high resolution, large field of view (FOV) and multispectral remote sensing is presented. An f/7.3 Korsch and two f/17.9 Cook three-mirror optical systems are integrated by sharing the primary and secondary mirrors, bias of the FOV, decentering of the apertures and reasonable structure arrangement. The aperture stop of the Korsch system is located on the primary mirror, while those of the Cook systems are on the exit pupils. High resolution image with spectral coverage from visible to near-infrared (NIR) can be acquired through the Korsch system with a focal length of 14 m, while wide-field imaging is accomplished by the two Cook systems whose focal lengths are both 13.24 m. The full FOV is 4°×0.13°, a coverage width of 34.9 km at the altitude of 500 km can then be acquired by push-broom imaging. To facilitate controlling the stray light, the intermediate images and the real exit pupils are spatially available. After optimization, a near diffraction-limited performance and a compact optical package are achieved. The sharing of the on-axis primary and secondary mirrors reduces the cost of fabrication, test, and manufacture effectively. Besides, the two tertiary mirrors of the Cook systems possess the same parameters, further cutting down the cost.

• Journal of Physiology & Pathology in Korean Medicine
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• v.16 no.3
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• pp.537-541
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• 2002

When a Kigong master concentrates the Qi at Yintang, Laogong(P8), Qihai(CV6) meridian points during Kigong state, the change of magnetic field around acupoints Yintang, Laogong points has been measured using DROS-SQUID apparatus. After smoothing process of the continuously measured magnetic signal around acupoints for a few minutes, we could observe that a series of peaks, magnitude of 1～2 pT and period of 5 sec, appeared and find that these peaks were clearly changed as if switch on and off according to Qi concentration state. Before Qi radiation, a series of the peaks measured on Yintang or Laogong point of a Kigong master shows one of either SW-ON state or SW-OFF state as initial state. During Qi radiation, its state becomes inverse of initial state. After Qi radiation, it returns to the initial state for some cases (called P type ; push button switch type) or it remains inversion state for other cases (called T type; toggle switch type). From the data of peaks measured at different position from the Qi concentration acupoint, we found that the Qi radiation on an acupoint makes the switching effect even not at the acupoint that Qi is concentrated but at the other acupoints that Qi is not concentrated.

• Journal of IKEEE
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• v.24 no.1
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• pp.260-268
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• 2020

This paper presents the high frequency resonant inverter of class D SEPP(Single-Ended Push Pull) type using LS-ZVS-LSTC, which can reduce the switching losses during the turn-on and turn-off switching time. The analysis of high frequency resonant inverter using LS-ZVS-LSTC(Low-loss Turn-off Snubber Capacitor) proposed in this paper is described in general by adopting the normalized parameters. The operating characteristics of the proposed high frequency resonant inverter were also evaluated by using the control parameters such as the normalized control frequency(μ), the normalized load time constant(τ), the coupling factor(κ) and so on. Based on the characteristic values through the characteristics of evaluation, an example of the design method of the 1.8[kW] class D SEPP type high frequency inverter is suggested, and the validity of the theoretical analysis is verified using the experimental data.

• International Commerce and Information Review
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• v.5 no.1
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• pp.39-59
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• 2003

The purpose of this paper is to examine the possibility of whether B2B e-marketplaces continue to grow. There are numerous barriers to the growth of e-marketplace, but certain key factors can push e-marketplaces beyond these obstacles. In the stage of generating traffic, it is essential to find a vertical area to attract buyers and sellers which can generate B2B transaction through e-marketplace. Generating traffic is possible only for e-marketplaces established by those who have vertical knowledges and strong off-line relationship in the vertical areas. In the stage of concentrating traffic, more attention should be given to reach critical mass and to increase transaction through e-marketplace. Currently, there seems to be a tendency that having major buyers as members of a e-marketplace is an true factor for the successful e-marketplace. Finally, to attain the locking traffic, e-marketplace needs to have the ability to generate revenue through B2B transaction. What we have learn from this study is that having the software-technology is not a sufficient condition to successfully operate B2B e-marketplace. It is important for e-marketplace to attract major players in order to increase B2B transaction, and also to make profit by them.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.1 s.190
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• pp.85-92
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• 2007

In the present study, three-dimensional motion analyses were performed to determine biomechanics of the lower extremity in unexpected missing foot steps for ten healthy young volunteers. In unexpected missing foot steps, the whole plantar surface of the foot or the heel contacted to the ground. A rapid ankle dorsiflexion was found right after missing foot steps and an increased plantarflexion moment was noted during loading response. After the unexpected situation, the breaking force increased rapidly. At this time, both tibialis anterior and soleus were simultaneously activated. Moreover, the range of motion at ankle, knee and hip significantly decreased during stance. In pre-swing, rectus femoris and biceps femoris prevented the collapse of the lower limbs. During late stance, propulsive forces decreased and thus, both plantarflexion moment and power generation were significantly reduced. On the opposite side, hip extension and pelvic upward motion during terminal swing were significant. Due to the shortened pre-swing, the energy generation at the ankle to push sufficiently off the ground was greatly reduced. This preliminary study would be helpful to understand the biomechanics of unexpected dynamic perturbations and valuable to prevent frequent falling of the elderly and patients with gait disorders.

• Korean Journal of Applied Biomechanics
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• v.13 no.3
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• pp.15-26
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• 2003

This study was conducted to investigate the performance times, CM position and CM speed, pole chord length and pole chord angle, whole body angular momentum(X axis), and grip width in pole vault event according to the event and phase; touch down, pole plant, take-off, maximum pole bending pole straight, pole release, peak height, and foot contact, pole contact, free flight. The pole vaulting of four male elite vaulters including six trial were filmed using two video digital cameras at 60 Hz at 56th national athletic match, and data were collected through the DLT method of three dimensional cinematography. In general the better jumper is, the longer the performance time is. And the greater CM speed is, and the better his transformation ability of CM horizontal speed into vertical speed is. As he uses a longer pole, his grip is higher, and it is a enough for him to rock back his body, so that he pulls and pushes the pole well keeping his hips close to. An greater maximum angular momentum and early positioning of the hips parallel to the bar makes his body far side of the bar and his bar clearance easier. Specially our national jumper needs to have more powerful braking force during foot contact phase, and take his body on the pole after maximum pole bending, and pull and push the pole strongly keeping his hips close to. Also he needs to have stronger muscular strength in order to control the longer pole and use the pole of proper tension more efficiently.